Re: [PATCH v3 06/10] compat/zlib: provide stubs for `deflateSetHeader()`

> The function `deflateSetHeader()` has been introduced with zlib v1.2.2.1,
> so we don't use it when linking against an older version of it. Refactor
> the code to instead provide a central stub via "compat/zlib.h" so that
> we can adapt it based on whether or not we use zlib-ng in a subsequent
> commit.
> 
> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  archive-tar.c        |  4 ----
>  compat/zlib-compat.h | 13 +++++++++++++
>  2 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/archive-tar.c b/archive-tar.c
> index e7b3489e1e..0edf13fba7 100644
> --- a/archive-tar.c
> +++ b/archive-tar.c
> @@ -473,9 +473,7 @@ static const char internal_gzip_command[] = "git archive gzip";
>  static int write_tar_filter_archive(const struct archiver *ar,
>  				    struct archiver_args *args)
>  {
> -#if ZLIB_VERNUM >= 0x1221
>  	struct gz_header_s gzhead = { .os = 3 }; /* Unix, for reproducibility */
> -#endif
>  	struct strbuf cmd = STRBUF_INIT;
>  	struct child_process filter = CHILD_PROCESS_INIT;
>  	int r;
> @@ -486,10 +484,8 @@ static int write_tar_filter_archive(const struct archiver *ar,
>  	if (!strcmp(ar->filter_command, internal_gzip_command)) {
>  		write_block = tgz_write_block;
>  		git_deflate_init_gzip(&gzstream, args->compression_level);
> -#if ZLIB_VERNUM >= 0x1221
>  		if (deflateSetHeader(&gzstream.z, &gzhead) != Z_OK)
>  			BUG("deflateSetHeader() called too late");
> -#endif
>  		gzstream.next_out = outbuf;
>  		gzstream.avail_out = sizeof(outbuf);
>  
> diff --git a/compat/zlib-compat.h b/compat/zlib-compat.h
> index 96a08811a9..2690bfce41 100644
> --- a/compat/zlib-compat.h
> +++ b/compat/zlib-compat.h
> @@ -7,4 +7,17 @@
>  # define deflateBound(c,s)  ((s) + (((s) + 7) >> 3) + (((s) + 63) >> 6) + 11)
>  #endif
>  
> +#if ZLIB_VERNUM < 0x1221
> +struct gz_header_s {
> +	int os;
> +};
> +
> +static int deflateSetHeader(z_streamp strm, struct gz_header_s *head)
> +{
> +	(void)(strm);
> +	(void)(head);
> +	return Z_OK;
> +}
> +#endif
> +
>  #endif /* COMPAT_ZLIB_H */